In recent years, digital cameras, which can easily capture an image into a personal computer, have become popularized with the spread of personal computers. It has also become common to incorporate a digital camera into information management systems, such as mobile computers, cellular phones and personal digital assistants (PDA: Personal Digital Assistant). With the spread of such digital cameras, a smaller digital camera has become to be demanded, and it becomes necessary to make a lens unit still smaller. The zoom lens of a large zoom ratio is required, and a zoom mechanism, which can realize such a zoom lens of a large zoom ratio, is demanded.
In order to make a lens unit small, proposals have been made in which the whole length of an image pickup lens does not change when zooming, and the camera size is minimized with a short depth of a digital camera. (Patent documents Nos. 1 and 2) These disclose a bending member on an optical path, and after folding an optical path substantially by 90 degrees, a following lens group forms an optical image on an image sensor.
In the two references mentioned above, the lens units surely become small. However, since the lens in the image sensor side of the bending member is moved to perform a zooming operation, the zoom ratio of the image pickup lens is small.
In order to solve this problem, the zoom lenses of a large zoom ratio have been proposed in which the lens in the object side of the bending member is moved to perform a zooming operation together with the lens in the image sensor side of the bending member. (Patent document 3)
Patent document No. 1: Unexamined Japanese Patent Application Publication No. 2000-131610
Patent document No. 2: Unexamined Japanese Patent Application Publication No. 2004-69808
Patent document No. 3: Unexamined Japanese Patent Application Publication No. 2004-102089